Pharmacological treatments that delay aging and the onset of age-related diseases would be highly valuable. Such compounds have been identified though the study of hormesis. Hormesis, or the hormetic effect, is an evolutionarily conserved phenomenon in which a mild stress can induce resistance to a more intense stress (autoprotection) and to different stresses (cross-protection), presumably by the induction of general protective mechanisms against environmental stress. The beneficial effects of this response have been shown to include lifespan extension. Understanding the mechanistic basis of a hormetic effect that increases lifespan and stress resistance will elucidate general mechanisms that control aging and suggest pharmacological interventions that can regulate this process. Plumbagin is a naturally occurring toxin that has been shown to elicit the hormetic effect in a wide range of organisms. Low doses of plumbagin induce tolerance to high doses in the budding yeast Saccharomyces cerevisiae, cause lifespan extension in the worm Caenorhabditis elegans, and protect mice against brain damage in a model of stroke. I found that low doses of plumbagin that induce tolerance to a high dose also significantly increase lifespan in S. cerevisiae. The pathways involved in plumbagin hormesis are not known in any organism. The goal of the proposed research is to determine the mechanism by which low doses of the plumbagin promote stress resistance and longevity in S. cerevisiae. Plumbagin is a naphthoquinone, a class of compounds that can react with cellular proteins. Plumbagin induces stress resistance at micromolar concentrations, about 0.1% the level required for other naphthoquinones to produce the same effect. Thus, plumbagin may be sensed by specific proteins, and I have identified two candidates that are required for plumbagin-induced autoprotection. In three specific aims, this project explores the hypothesis that low levels of plumbagin are sensed by a small number of proteins which subsequently initiate a signaling cascade to induce autoprotection and lifespan extension. Aim 1 will determine if the plumbagin hormetic pathway is the same as, or distinct from, pathways for other known lifespan-extending and stress protection treatments such as reduced calorie intake, heat stress and oxidative stress. Aim 2 will test if candidate plumbagin sensing proteins form covalent bonds with plumbagin. Aim 3 will determine if activation of signaling pathways associated with candidate sensors is sufficient to recapitulate the hormetic effects of plumbagin, and will identify genes required for plumbagin-induced stress resistance using whole genome approaches. Successful completion of this work will show how a small molecule can extend lifespan, and will provide essential knowledge required to devise pharmacological interventions that can improve human health and longevity.